1. Field
The field relates to an organic light emitting display and a driving method thereof, and more particularly to an organic light emitting display capable of displaying an image with uniform luminance regardless of deterioration of an organic light emitting diode and threshold voltage or mobility of a drive transistor, and a driving method thereof.
2. Discussion of Related Technology
In recent years, a variety of flat panel displays of reduced weight and volume, when compared to a cathode ray tube have been developed and commercialized. A flat panel display may take the form of a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an organic light emitting display (OLED), etc.
Among the flat panel displays, the organic light emitting display uses an organic light emitting diode to display an image, the organic light emitting diode generating light by means of the recombination of electrons and holes. Such an organic light emitting display has advantages in that it has a rapid response time and is also driven with low power consumption.
FIG. 1 is a circuit view showing a pixel of a conventional organic light emitting display.
Referring to FIG. 1, the pixel 4 includes an organic light emitting diode (OLED), data lines (Dm), and a pixel circuit 2 connected to the scan lines (Sn) to control the organic light emitting diode (OLED).
An anode electrode of the organic light emitting diode (OLED) is connected to the pixel circuit 2, and a cathode electrode is connected to the second power source (ELVSS). Such an organic light emitting diode (OLED) generates a predetermined luminance to correspond to an electric current supplied from the pixel circuit 2.
The pixel circuit 2 controls an electric current capacity supplied to the organic light emitting diode (OLED) to correspond to a data signal supplied to the data lines (Dm) when a scan signal is supplied to the scan lines (Sn). For this purpose, the pixel circuit 2 includes a second transistor (M2) connected between the first power source (ELVDD) and the organic light emitting diode (OLED); a first transistor (M1) connected between the second transistor (M2) and the data lines (Dm) and the scan lines (Sn); and a storage capacitor (Cst) connected between a gate electrode and a first electrode of the second transistor (M2).
A gate electrode of the first transistor (M1) is connected to the scan lines (Sn), and a first electrode is connected to the data lines (Dm). A second electrode of the first transistor (M1) is connected to one side terminal of the storage capacitor (Cst). Here, the first electrode is either a source electrode or a drain electrode, and the second electrode is the electrode which is different from the first electrode. For example, if the first electrode is a source electrode, the second electrode is a drain electrode. When a scan signal is supplied from the scan lines (Sn), the first transistor (M1) connected to the scan lines (Sn) and the data lines (Dm) is turned on to supply the data signal from the data lines (Dm) to the storage capacitor (Cst). As a result, the storage capacitor (Cst) charges a voltage corresponding to the data signal.
The gate electrode of the second transistor (M2) is connected to one terminal of the storage capacitor (Cst), and the first electrode is connected to the other terminal of the storage capacitor (Cst) and to the first power source (ELVDD). The second electrode of the second transistor (M2) is connected to the anode electrode of the organic light emitting diode (OLED). The second transistor (M2) controls the electric current so as to correspond to the voltage stored in the storage capacitor (Cst), the electric current flowing from the first power source (ELVDD) to the second power source (ELVSS) via the organic light emitting diode (OLED). In response, the organic light emitting diode (OLED) generates light according to the amount of electric current supplied from the second transistor (M2).
However, an organic light emitting display having a pixel such as that of FIG. 1 has a disadvantage that it is difficult to display an image having a desired luminance due to the changes in current caused by the deterioration of the organic light emitting diode (OLED). The organic light emitting diode deteriorates with the passage of time, and therefore, the organic light emitting diode generates light of reduced luminance over time despite receiving the same level of a data signal. Also, the conventional organic light emitting display has a problem that it does not display an image having a uniform luminance due to non-uniformity in the threshold voltage and/or mobility of the drive transistors (M2) in each of the pixels 4.